Scanning electron microscope

ABSTRACT

A scanning transmission electron microscope incorporating a lens system for forming a diffraction pattern of the electrons transmitted through a crystalline specimen and a detector for detecting transmitted electrons to obtain a scanning microscope image. The scanning microscope image and its corresponding diffraction pattern are observed simultaneously thereby facilitating the observation of variations in said specimen, for example, as may occur with the passage of time or a change in temperature.

United States Patent 1191 Koike et al.

[451 Nov. 19, 1974 SCANNING ELECTRON MICROSCOPE [75] Inventors: Hirotami Koike; Katsuyoshi Ueno,

[21] Appl. No.: 327,615

[30] Foreign Application Priority Data 3,560,739 2/1971 Wolff 250/311 3,660,657 5/1972 Brookes 313/84 OTHER PUBLICATIONS The Arizona lMcV Transmission Scanning Electron Microscope, Strojnik, Proceedings of 5th Annual SEM Symp., part 1, April, 1972.

Primary ExaminerJames W. Lawrence Assistant Examiner-C. E. Church Attorney, Agent, or Firm-Webb, Burden, Robinson & Webb Oct. 23, 1972 Japan 47-10593] [52 us. c1. 250/306, 250/310 ABSTRACT [5 C]- A anning transmission electron microscope incorpo- [58] Field of Search 250/311, 310, 306; 313/ 4 rating a lens system for forming a diffraction pattern of the electrons transmitted through a crystalline spec- References Clmd imen and a detector for detecting transmitted elec- UNITED STATES PATENTS trons to obtain a scanning microscope image. The 2,438,971 4/1948 Hillier 313/84 Scanning microswpe image and its corresponding 3,090,864 5/1963 Takahashi 250/306 fraction Pattern are Observed Simultaneously thereby 3,180,986 4/1965 Grigson .1 250/306 facilitating the observation of variations in said speci- 3,225,192 12/1965 Katagiri 250/306 men, for example, as may occur with the passage of 3,370,168 Komoda time or a change in temperature 3,502,870 3/1970 Fujiyasu 250/310 3,508,049 4/1970 Bische 250/311 8 Claims, 9 Drawing Figures 6 SCANNING El CURRENT SUPPLY CURRENT SUPPLY are supra"?- PMENTL- 118V 1 93974 sum 8 or a SCANNING CURRENT SUPPLY CURRENT SUPPLY CANN 1 MG CURRENT SUPPLY SCANNING ELECTRON MICROSCOPE Our invention provides a scanning transmission electron microscope capable of simultaneously displaying a scanning microscope image of the electrons transmitted through the specimen on a cathode-ray tube or the like and also displaying a diffraction pattern.

In the prior art relating to conventional transmission type electron microscopes for displaying microscope images of crystalline specimens and their corresponding diffraction patterns on a fluorescent screen or photographic plate, either the microscope image or the diffraction pattern are changed by adjusting the image forming lens system. As a result, it is impossible to observe both the microscope image and its corresponding diffraction pattern at the same time.

This being the case, microscopes of this type, heretofore described, are incapable of permitting the observation of specimen variation with the passage of time; e.g., phase transformation changes in crystalline structure or the growth of the crystalline formation by heating or cooling the specimen. As such, microscopes of this type related to in the prior art are restricted in application.

An advantage of this invention, therefore, is to remove this restriction by providing a scanning transmission electron microscope capable of displaying a scanning image produced by the transmitted electrons and its corresponding diffraction pattern simultaneously.

Other objects and advantages of the invention will become apparent from the following detailed descrip tion made with reference to the drawings wherein:

FIG. 1 is a schematic drawing of a scanning electron microscope according to this invention;

FIG. 2 is a detailed schematic drawing showing the structural arrangement of the objective lens forming part of the lens system of the microscope shown in FIG.

FIG. 3 is a diagrammatic representation showing the beam path and magnetic field produced by the objective lens shown in FIG. 2;

FIG. 4 is a schematic diagram showing the electron beam path in the microscope described in FIG. 1;

FIG. 5 is a schematic diagram showing the electron optical system of another embodiment of this invention;

FIG. 6 is a schematic drawing showing another structural arrangement of the objective lens shown in FIG.

FIG. 7 is a schematic drawing showing still another structural arrangement of the objective lens shown in FIG. 2;

FIG. 8 is a schematic diagram showing an embodiment for displaying the diffraction pattern on a cahoderay tube; and,

FIG. 9 is a schematic diagram showing another embodiment for displaying the diffraction pattern on a cathode-ray tube.

Referring to FIG. 1, an electron gun I generates an electron beam which is condensed and focused by condenser lenses 2 and 3 and an objective lens, 4 so as to irradiate a crystalline specimen held by the holder 5 which is supported by a specimen stage 5a with very small diameter electron beam. The beam is made to scan over the specimen in a two-dimensional raster by means of deflecting coils 6 and their scanning current supply 7 and the objective lens 4. Moreover, the electron beam transmitted through and diffracted by the specimen is formed into a diffraction pattern on a fluorescent screen 8 by means of the magnetic field of the objective lens 4, said pattern being observed through a window 9 of an observation chamber 10. The transmitted electrons which reach the center of the fluorescent screen 8 pass through a small aperture 11 and are detected by an electron detector 12.

The output signal from the detector 12 is supplied to the brightness control grid of a cathode-ray tube 13 via an amplifier 14. Since deflecting coils 15 forming part of the cathode-ray tube 13 are supplied with deflecting current from the same current supply source 7 as the deflecting coil 6, a conventional scanning microscope image can be displayed on the screen of the cathoderay tube 13.

Deflecting coils 16 attached to the upper part of the observation chamber 10 and their current supply 17' is utilized to deflect the electron beam so that the desired diffraction pattern spot passes through the aperture 11. In this case, a means for moving the detector 12 and its aperture 11 mechanically may be used instead of deflecting coil 16 and its current supply 17.

FIG. 2 shows the structure of the objective lens 4 in detail. The lens consists of an exciting coil 18, a yoke 19 and pole pieces 20 and 21 and a non-magnetic spacer 22. The pole pieces 20 and 21 constitute a magnetic flux gap by means of the spacer 22. A crystalline specimen 23 is located between the pole pieces 20 and 21 and the deflecting coil 6 for scanning the electron beam over the specimen is attached to the upper part of the pole piece 20.

The strength of the magnetic field along the optical axis is indicated by the distance of the line 24 from the axis in FIG. 3. The electron beam path 25 in the above pole pieces are indicated in FIG. 3 in an exaggerated manner. In the figure, the magnetic field 24 is so strong in the area below the specimen that the center beam of the electrons transmitted through the specimen crosses the optical axis 26 at least twice; i.e., at points A and B shown in FIG. 3.

FIG. 4 is a schematic diagram showing the electron beam path in the microscope described in FIG. 1. In the figure, apparent lenses 4a, 4b and 4c are produced by the strong magnetic field 24 of the objective lens 4 as shown in FIG. 3. The electron beam generated by the electron gun is condensed by the apparent lens 4a in addition to being condensed by condenser lenses 2 (not shown in FIG. 4) and 3 so as to minimize the crosssectional diameter of the electron on the specimen. The beam is then deflected by deflecting coil 6 and the apparent lens 4a. Since the said deflecting coil 6 is located at the front focal point of the apparent lens 4a, the electron beam irradiates the specimen perpendicularly. By so doing, the electron beams 25b, 25c are diffracted by the specimen 23 while the center beam 25a remains undiffracted. These beams form a diffraction pattern at positions 27 and 28; i.e., at the positions where the center beam crosses the optical axis 26. In this case, if the crystalline structure is the same regardless of the scanning position the diffraction pattern formed on the screen 8 will remain stationary whenever the electron beam scans the specimen.

FIG. 5 is a schematic diagram showing the electron optical system of another embodiment of this invention. In this embodiment, two pairs of coils 6a and 6b are located above the front focal point of the apparent lens 4a so as to deflect the electron beam twice, thereby varying the angle at which the electron beam crosses the optical axis 26 at said front focal point of the apparent lens 4a. In this way, the beam approaches the specimens perpendicular to the surface thereof.

FIG. 6 is a schematic drawing showing another structural arrangement of the objective lens shown in FIG. 2. In this arrangement, an additional magnetic pole piece 29 is inserted between pole pieces and 21, resulting in a single magnetic flux path with two magnetic flux gaps. Since the crystalline specimen 23 is placed in the pole piece 29, the upper magnetic flux gap acts in the same way as the apparent lens 4a in FIG. 4 and the lower magnetic flux gap acts in the same way as the apparent lens 4b or the apparent lenses 4b and 4c in combination.

FIG. 7 is a schematic diagram showing still another structural arrangement of the objective lens shown in FIG. 2. In this case, an exciting lens coil 30, yoke 31, magnetic pole pieces 32 and 33, including spacer 34, have been added to the original structure. By so doing, there are two magnetic flux paths and two magnetic flux gaps. With this arrangement, if the magnetic field strength in the upper gap is as strong as that shown in FIG. 3, the magnetic field at the lower gap acts as an extra lens and the diffraction pattern is further enlarged. In this case, the center of the electron beam transmitted through the specimen crosses the optical axis more than twice and the diffraction pattern can be formed at any of the planes where the electron beam crosses the optical axis. Moreover, if the magnetic field strength in the upper gap is insufiicient, the magnetic field at the upper gap acts as the apparent lenses 4a and 4b and the magnetic field at the lower gap acts as the apparent lens 40.

FIG. 8 is a schematic diagram showing an embodiment for displaying the diffraction pattern on a cathode-ray tube. In this embodiment, a small electron detector 35, for example, a semiconductor detector, is located at the center of the plane 28 where the diffraction pattern is formed, so as to produce a signal for the scanning microscope image. A second electron detector 36, complete with aperture 37, is arranged below the electron detector 35. In addition, deflecting coils 38 for scanning the entire diffraction pattern over the aperture 37 are located between said detectors 35 and 36. The signal produced by the detector 36 is supplied to the brightness control grid of a cathode-ray tube 39 via an amplifier 40. Moreover, since the scanning current supply 41 is common to both deflecting coils 38 and deflecting coils 42 of the cathode-ray tube 39, the diffraction pattern is displayed on the cathode-ray tube 39. In this case, it is possible to display a diffraction pattern by mechanically scanning the detector 36, complete with aperture 37, over the diffraction pattern instead of scanning the diffraction pattern with the aid of the deflecting coils 38.

FIG. 9 is a schematic diagram showing another embodiment for displaying the diffraction pattern on a cathode-ray tube in which an image pick-up tube 43 is used instead of the detector 36. In this case, deflecting coils 38 are dispensed with the deflector coils 44 incorporated in the image pick-up tube being used in lieu. By so doing, the diffraction pattern formed on the plane 28 is displayed on the cathode-ray tube 39.

Having thus described the invention with the detail and particularity as required by the Patent Laws, what is desired protected by Letters Patent is set forth in the following claims.

We claim:

1. A scanning transmission electron microscope and electron diffraction device having a lens and deflection system defining an electron optical axis and comprising means for generating an electron beam directed along the optical axis, means for condensing said electron beam, an objective lens comprising a magnetic flux creating coil and associated pole pieces for creating a magnetic lens in the gap between the pole pieces, means for positioning a transmission specimen along the optical axis in the specimen plane within the gap between the pole pieces of the objective lens, the intensity of the magnetic flux in said gap being sufficient to form a first apparent lens just before the specimen plane and a second apparent lens thereafter, said objective lens system causing the electron beam to cross the electron optical axis at least twice after passing through the specimen plane, means comprising at least one deflection stage for deflecting the electron beam through a point on the front focal plane of the first apparent lens such that the beam scans the specimen substantially perpendicular thereto, a detecting means for detecting the transmitted electron beam, said detecting means being placed on any plane perpendicular to the optical axis where the center of the electron beam crosses the optical axis at the second or more crossing points, a first display means to which the signal from said detecting means is supplied, said display means being synchronized with said deflecting means and a second display means for displaying the diffraction pattern formed on the plane where the center of the electron beam crosses the optical axis at the second or more crossing points.

2. A scanning transmission electron microscope as described in claim 1 wherein said display means for displaying the diffraction pattern consists of a fluorescent screen.

3. A scanning transmission electron microscope as described in claim 1 wherein said display means for displaying the diffraction pattern consists of an image pickup tube and a display tube, said display tube being synchronized with said image pick-up tube.

4. A scanning transmission electron microscope as described in claim 1 wherein said display means for displaying the diffraction pattern consists of an electron detector and a deflecting means for scanning the diffraction pattern over said detector and a display tube for displaying the signal of said detector, said display tube being synchronized with said deflecting means.

5. A scanning transmission electron microscope having a lens and a deflection system defining an electron optical axis comprising means for generating an electron beam directed along the optical axis, means for condensing said electron beam, an objective lens consisting of a magnetic flux creating coil and associated pole pieces for creating a magnetic lens in the gap between the pole pieces, means for positioning a transmission specimen along the optical axis in a specimen plane within the gap between the pole pieces of the objective lens, the intensity of the magnetic flux in said gap being sufficient to form a first apparent lens before the specimen plane and a second apparent lens thereafter, said objective lens system causing the electron beam to cross the electron optical axis at least twice after passing through the specimen plane, means comprising at least one deflection stage for deflecting the described in claim 5 wherein said lens system consists of a single magnetic flux path.

7. A scanning transmission electron microscope as described in claim 6 wherein said single magnetic flux path has a single magnetic flux' gap in which a magnetic field having plural lens action is generated.

8. A scanning transmission electron microscope as described in claim 6 wherein said single magnetic flux path has two magnetic flux gaps each gap having at least single lens action.

. UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Eeeene No. 3, 849, 647 Dated November 19, 1974 Inventor(s) Hirotami Koike and Katsuyoshi Ueno It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the first page of the vpatent in the line listing the Serial Number:

' ---January 22, 1973". should read anuar 26, 1973".

Column 1 Line 54, --cahode should read --ca1:hode--.

Column 2 Line 50, After --e1ectron-.- insert --bearn--.

- Signed and sealed this 21st day of January'l975.

(SEAL) Attest:

MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents F ORM P04 050 (10-69) uscoMM-oc scenes9 ".5. GOVERNMENT PRINTING OFFICE Z |969 0-355334 

1. A scanning transmission electron microscope and electron diffraction device having a lens and deflection system defining an electron optical axis and comprising meAns for generating an electron beam directed along the optical axis, means for condensing said electron beam, an objective lens comprising a magnetic flux creating coil and associated pole pieces for creating a magnetic lens in the gap between the pole pieces, means for positioning a transmission specimen along the optical axis in the specimen plane within the gap between the pole pieces of the objective lens, the intensity of the magnetic flux in said gap being sufficient to form a first apparent lens just before the specimen plane and a second apparent lens thereafter, said objective lens system causing the electron beam to cross the electron optical axis at least twice after passing through the specimen plane, means comprising at least one deflection stage for deflecting the electron beam through a point on the front focal plane of the first apparent lens such that the beam scans the specimen substantially perpendicular thereto, a detecting means for detecting the transmitted electron beam, said detecting means being placed on any plane perpendicular to the optical axis where the center of the electron beam crosses the optical axis at the second or more crossing points, a first display means to which the signal from said detecting means is supplied, said display means being synchronized with said deflecting means and a second display means for displaying the diffraction pattern formed on the plane where the center of the electron beam crosses the optical axis at the second or more crossing points.
 2. A scanning transmission electron microscope as described in claim 1 wherein said display means for displaying the diffraction pattern consists of a fluorescent screen.
 3. A scanning transmission electron microscope as described in claim 1 wherein said display means for displaying the diffraction pattern consists of an image pick-up tube and a display tube, said display tube being synchronized with said image pick-up tube.
 4. A scanning transmission electron microscope as described in claim 1 wherein said display means for displaying the diffraction pattern consists of an electron detector and a deflecting means for scanning the diffraction pattern over said detector and a display tube for displaying the signal of said detector, said display tube being synchronized with said deflecting means.
 5. A scanning transmission electron microscope having a lens and a deflection system defining an electron optical axis comprising means for generating an electron beam directed along the optical axis, means for condensing said electron beam, an objective lens consisting of a magnetic flux creating coil and associated pole pieces for creating a magnetic lens in the gap between the pole pieces, means for positioning a transmission specimen along the optical axis in a specimen plane within the gap between the pole pieces of the objective lens, the intensity of the magnetic flux in said gap being sufficient to form a first apparent lens before the specimen plane and a second apparent lens thereafter, said objective lens system causing the electron beam to cross the electron optical axis at least twice after passing through the specimen plane, means comprising at least one deflection stage for deflecting the electron beam through a point on the front focal plane of the first apparent lens such that the beam scans the specimen substantially perpendicular thereto, means for detecting the transmitted electron beam, said detecting means being placed on any plane perpendicular to the optical axis where the beam crosses the optical axis at the second or more crossing points and a display means to which the signal from said detecting means is supplied, said display means being synchronized with said deflecting means.
 6. A scanning transmission electron microscope as described in claim 5 wherein said lens system consists of a single magnetic flux path.
 7. A scanning transmission electron microscope as described in claim 6 wherein said single magnetic flux path has a single magnetic fLux gap in which a magnetic field having plural lens action is generated.
 8. A scanning transmission electron microscope as described in claim 6 wherein said single magnetic flux path has two magnetic flux gaps each gap having at least single lens action. 